The long-term goal is to identify the physiological functions of the peptide hormones which control reproductive behaviors. Recent research demonstrates that the reproductive behaviors of certain animals can be influenced by injections of any of the following peptide hormones: luteinizing hormone-releasing hormone (LHRH), adrenocorticotropin (ACTH), arg vasotocin (AVT), prolactin and endorphin. But the specific actions and interactions of these peptides in modulating reproductive behaviors remain unknown. The proposed research will use the extirpation-replacement experimental paradigm, microinjections of hormones or their antagonists into specific regions of the brain, and measurement of endogenous concentrations by radioimmunoassay procedures. These studies will determine the functional relationships between the gonadal steroid hormones (e.g. estradiol and dihydrotestosterone) and the peptides listed above. Other experiments will identify the functional relationships among the peptides, determining for example, whether AVT enhances the behaviors by causing a localized release of LHRH. Many gaps in our understanding of the neurochemical pathways which control the propensity to exhibit reproductive behaviors will be filled by these studies. The specific behavior for study will be the reproductive behavior of a species of urodele amphibian. The simplified nervous system of amphibians, the stereotyped nature of their reproductive behavior, and the recent evidence from my laboratory indicating that the same hormones that modify the reproductive behaviors of mammals also modify behaviors of this amphibian makes this animal an advantageous research model.